Decision Rules Related to ISO/IEC 17025:2017

1
Decision Rules Related to ISO/IEC
170252017Maryam SouraniPh.D Student in
Analytical Chemistry Email Sourani2009_at_gmail.com
2
Resources

1. Decision rule, ISO/IEC 170252017
2. Compliance with specification, ILAC-G081996
   (Rev. 2009)
3. Uncertainty info. in compliance assess.
   EURACHEM/CITAC 2007
4. The role of measurement uncertainty in conformity
   assessment , BIPM-JCGM 1062012
5. Decision rules applied to conformity assessment,
   EUROLAB- Technical Report No. 01/2017
6. Uncertainty in conformity assess. decisions, OIML
   G 192017
7. Decision rules and statements of conformity,
   ILAC-G0809/2019
8. GUIDELINES FOR DECISION RULES CONSIDERING
   MEASUREMENT UNCERTAINTY IN DETERMINING
   CONFORMANCE TO SPECIFICATIONS, ASME
   B89.7.3.1-2001
9. Decision rules for verifying conformity or
   nonconformity with specifications, ISO 14253-1
10. The Expression of Uncertainty in Testing, UKAS
    lab 12, Edition 3 November 2019
11. DETERMINATION OF CONFORMANCE WITH SPECIFICATIONS
    USING MEASUREMENT UNCERTAINTIES POSSIBLE
    STRATEGIES, EUROLAB Cook Book Doc No. 8

3
Change of Thinking/Approach
4
What is risk ?
ISO Guide 732009, Risk management - Vocabulary
Clause 1 Terms related to risk 1.1 risk
effect of uncertainty on objectives. Notes - An
effect is a deviation from the expected -
positive and/or negative. -Risk is often
expressed in terms of a combination of the
consequences of an event and the associated
likelihood of occurrence. -Uncertainty is the
state of deficiency of information related to,
understanding/knowledge of, an event, its
consequence, or likelihood. -Objectives
Expected results (ISO 90012015)
5
Decision Rule ISO/IEC 170252017
Clause 3 Terms and definitions 3.7 decision
rule Rule that describes how measurement
uncertainty is accounted for when stating
conformity with a specified requirement.
6
Risk - Uncertainty - Decision Rule
Decision rule gt measurement uncertainty gt
conformity of result Risk gt measurement
uncertainty gt expected result Decision rule gt
level of risk gt conformity of result (compliance
with specification)
7
Decision Rule ISO/IEC 170252017 Clause 5
Structural Requirements 5.3 The lab. shall
define and document the range of lab. activities
for which it conforms with this document. The
lab. shall only claim conformity with this
document for this range of lab. activities, ..
8
Clause 6 Resource requirements
Decision Rule ISO/IEC 170252017
6.2 Personnel 6.2.6 The lab. shall authorize
personnel to perform specific lab. activities,
. b) Analysis of results, including statements
of conformity or opinions and interpretations
9
Decision Rule ISO/IEC 170252017
Clause 7 Process requirements 7.1 Review of
requests, tenders and contracts 7.1.3 When the
customer requests a statement of conformity to a
specification or standard for the test or
calibration (e.g. pass/fail, in-tolerance/out-tol
erance ), the decision rule shall be clearly
defined. Unless inherent in the requested
specification or standard, the decision rule
selected shall be communicated to, an agreed
with, the customer.
10
Decision Rule ISO/IEC 170252017
7.8 Reporting of results 7.8.3 Specific
requirements for test reports 7.8.3.1 Test
reports shall, where necessary for the
interpretation of the test results, include the
following c) Where applicable, the
measurement uncertainty present in the same unit
as that of the measurand or in a term relative to
measurand ( e.g. percent ) when - It is
relevant to the validity or application of the
test results. - The measurement uncertainty
affects conformity to a specification limit.
11
Decision Rule ISO/IEC 170252017
7.8.6 Reporting statements of conformity
7.8.6.1 When a statement of conformity to a
specification or standard is provided, the lab.
shall document the decision rule employed, taking
into account the level of risk (false accept and
false reject and statistical assumptions)
associated with the decision rule employed and
apply the decision rule.
12
Decision Rule ISO/IEC 170252017
7.8.6.2 The lab. shall report on the statement of
conformity, such that the statement clearly
identifies . c) The decision rule applied
(unless it is inherent in the requested
specification or standard).
13
ILAC-G082009 uses the measurement with 95
coverage interval in conformity assessment
14
ILAC-G082009 uses the measurement with 95
coverage interval in conformity assessment.
15
EURACHEM/CITAC Guide 2007, Use of uncertainty
information in compliance assessment (Guard band
decision rules, High confidence of correct
acceptance)
Focusing on correct acceptance, Low risk of
false acceptance, Guarded acceptance
g 1.64 u ---gt 5 false acceptance g 2.33
u ---gt 1 false acceptance
16
New ISO/IEC 170252017 and Decision Rule
Graphic presentation on a stringent Acceptance
zone and a relaxed Rejection zone for a
specification with an upper limit
17
EURACHEM/ CITAC 2007, Decision rules based on
guard bands (High confidence of correct
rejection)
Focusing on correct rejection, low risk of false
rejection, guarded rejection
18
One-Tailed Standard Normal Distribution
z ? (z) Coverage Interval False Acceptance
0.84 0.8 80 20
1.00 0.841 84.1 15.9
1.28 0.9 90 10
1.64 0.95 95 5
1.96 0.975 97.5 2.5
2.33 0.99 99 1
3.08 0.999 99.9 0.1
y Tu
?(z) Cumulative Standard Normal Distribution
from -? to Z NORM.S.DIST(z, TRUE) , EXCEL
Spread Sheet z (Tu y) / u u Standard
Uncertainty, U Expanded Uncertainty Tu Upper
Specification Limit
19
(No Transcript)
20
BIPM-JCGM 1062012, Evaluation of measurement
data- The role of measurement uncertainty in
conformity assessment Clause 3 Terms and
definitions 3.3 Terms related to conformity
assessment 3.3.11 guard band interval between a
tolerance limit and a corresponding acceptance
limit.
21
BIPM-JCGM 1062012

• 3.3.12 decision rule
• documented rule that describes how measurement
  uncertainty will be accounted for with regard to
  accepting or rejecting an item, given a specified
  requirement and the result of a measurement.

22
BIPM-JCGM 1062012
Single Upper Tolerance Limit Pc ?((Tu y) /u )
conformity probability
Figure shows upper tolerance limit and rejection
zone
23
BIPM-JCGM 1062012
Single Lower Tolerance Limit Pc 1 - ?((TL
y)/u ) conformity probability
Figure shows single lower tolerance limit, TL
24
BIPM-JCGM 1062012
Pc ?((Tu y)/u ) - ?((TL y)/u ) conformity
probability
Figure shows lower tolerance limit, upper
tolerance limit and rejection zone
25
BIPM-JCGM 1022012
Figure shows Guard band (yellow area). Guarded
acceptance decision rule reduces false
acceptance of non-conforming item (consumers
risk).
26
BIPM-JCGM 1062012
Figure shows consumers risk vs guard band
multiplier
27
BIPM-JCGM 1062012
Figure shows relationship of consumers and
producers risk
28
BIPM-JCGM 1062012
Cm T / 4 u Measurement Capability Index u
standard measurement uncertainty
29
EUROLAB Tech. Report No. 01/2017, Decision rules
applied to conformity assessment
( ?? )
Over estimated entity value
(??)
Supplier income and cost due to conformity
(adapted from L.R. Pendrill, 2007)
30
EUROLAB Tech. No. 01/2017
Decision (Test value)
(True Value) Accept H0 Reject H0
H0 (True) Correct decision Type l error (?? error) (False positive, False rejection) Producer risk
H0 (False) Type ll error (?? error) (False negative, False acceptance) Consumer risk Correct decision
Conformity probabilities related to correct/
incorrect decision
31
Example 1
A measurement value y 2.7 mm with a standard
uncertainty, u 0.2 mm
given a single tolerance upper limit, TU 3.0
mm, conformity spec. 95 , this entity is
found to conform with the spec. or not? Decision
rule will be Acceptance if hypothesis H0 Pr( y
? 3.0mm ) is true. Conformity probability, Pc
Pr( y ? TU ) ?((TU y ) / u) ?((3.0-2.7)/
0.2) ?(1.5) ? 0.933 (93.3) lt 0.95 (95)
. Then the hypothesis H0 is false and the
entity does not conform with the spec. (the
decision is of non-conformity). (Adapted from
EUROLAB Tech. Report No.1/2017)
? 0.05
Pc 1- ? 0.95 2.7 3.0
32
decision limit -guard band single upper tolerance
limit
TU y
) 1 - ? conformity probability
?(
??
TU y
) ?¹ (1- ?)
(
??
??
where g guard band
Au y TU - ?? ? ?¹ (1-?) Au decision
limit u standard uncertainty
g
Au TU
33
(No Transcript)
34
(No Transcript)
35
OIML G 192017, The role of measurement
uncertainty in conformity assessment decision in
legal metrology
Conformity Criterion What is the prob. Of the
error of indication (E) lie inside of the
conformance zone? Example 6 The indicated value
of length (LI) of Caliper under test is 10.006 mm
when the value of reference guage block (LR) is
10.003 mm. The measured value of the error of
indication is then E LI - LR 0.003 mm The
standard uncertainty of the error of indication,
u, is 0.0018 mm If the maximum permissible error,
MPE, for this test is 0.005 mm, then z is
calculated as z (MPE E)/ u (0.005
0.003)/ 0.0018 1.11 From the cumulative
standard normal distribution table the cumulative
probability is 0.8665 (86.7 ). Thus, the risk
of false acceptance is 1 0.867 0.133
(13.3). If the decision limit (non-conformity)
is 2, then the maximum permissible uncertainty
test would fail . Another way to state conformity
is to use Tolerance Uncertainty Ratio (TUR) TUR
MPE / u 0.005/0.0018 2.78 The typical value
of TUR is 3, therefore the above maximum
permissible uncertainty test would fail.
36
(No Transcript)
37
ILAC-G809/2019, Guidelines on Decision Rules and
Statement of Conformity
Decision Rules Guard Band Specific Risk
6 sigma 3 U lt 1 ppm PFA
3 sigma 1.5 U lt 0.16 PFA
ILAC G82009 rule 1 U lt 2.5 PFA
ISO 14253-12017 0.83 U 5 PFA
Simple acceptance 0 lt 50 PFA
Uncritical -U Item rejected for measured value gt AL TL U lt 2.5 PFR
Customer defined r U Customers define arbitrary multiplier , r .
PFA Prob. of False Accept, U Expanded
Uncertainty, TL Tolerance Limit
PFR Prob. of False Reject AL Acceptance Limit
38
(No Transcript)
39
(No Transcript)